The subject of the invention is a process for the preparation of any type of patterned, monochromatic or polychromatic, optical color filter, such as is used, for example, for color separation in devices for making color images or particularly in systems for the reproduction of such images (displays).
Most of such color filters are finely patterned, that is, the structural elements are often only a few microns large. Depending on the use, these elements are in the form of stripes, circles or other geometric figures. Most are required for filters with closely adjoining areas of different colors.
Many processes are known for the preparation of such color filters. The methods used include screen printing, color photography based on silver halides, diazo processes, the transfer of preformed polychromatic patterns onto a common substrate, imagewise ablation of color layers by laser, washoff after photocrosslinking, applying color to lithographically formed patterns from colorless binders, and others.
Similarly known are processes in which finely divided dyes or dyed compositions are coated in the form of the desired pattern onto the substrate. Thus, European Patents 01 13 237 and 01 57 486 disclose the preparation first of a patterned, conductive layer on an insulating substrate and then coating electrophoretically on the conductive areas a dyed polymer layer from an aqueous solution containing a polymer and a dye. Various conductive areas insulated from one another can be provided successively with coatings of various colors in suitable electrophoretic baths. If the conductive areas are later to serve as electrodes in liquid crystal cells, then the electrical field is partially shielded by the polymer layer, which decreases the sensitivity of the cell.
German Patents 27 58 209 and 24 29 615 disclose negative-working light-sensitive layers, the exposed areas of which are tonable with a powdered color to produce an image. The layers described therein can also contain a plasticizer. The use of negative-working layers for polychromatic images offers the advantage that, in the first step, the unexposed and untoned areas retain their light-sensitivity and can be toned in a succeeding step with another color after exposure of another pattern. This process can be repeated until the entire layer is toned. However, patterns prepared by this process on transparent supports are not suitable as color filters, because they scatter too much light. In addition, they are unstable to many solvents, so that further processing to liquid crystal cells, for example, the application of equalizing layers, is possible only with limitations.
The problem involved in the invention is the development of a process in which color filters with low light scatter and good stability to mechanical and chemical stresses can be prepared in a simple manner by the use of negative-working, light-sensitive, tonable layers.